It is proposed to measure the mechanical behavior of bone tissue taken from dogs that have been fed a fluorine-enriched diet. Six-week-old dogs will be placed on a high fluoride diet, sacrificed at four-week intervals and bone specimens machined from the femur, tibia and humerus for mechanical testing. In addition, the rickettic calf model will be further developed by separating the calf from the cow at an earlier age so that the calf may be fed a vitamin D-deficient diet for a longer period of time. Bone test specimens will be machined and mechanically tested for tension, compression and torsional strengths.